1. Field of the Invention
This invention relates to the field of consumer devices, and in particular to techniques for preventing or discouraging the illicit duplication of copy protected material.
2. Description of Related Art
Techniques are continually being proposed and developed to prevent or discourage the illicit duplication of copy-protected material, such as commercial music recordings. These techniques generally attempt to limit the number of copies that can be made from a legitimate copy of the copy-protected material. At the same time, the purchaser of this legitimate copy expects to have unlimited rights for copying this material for his or her private purposes. For example, the typical purchaser has access to multiple means for playing and recording the material, and expects to be able to play the purchased material on each of these means, without constraints.
Increasingly common in the art is the use of flash memory cards to record content material for playback on small portable devices. These flash memory cards, or similar electronic memory devices, have an advantage over conventional recording media such as discs or tapes, in that they contain no moving parts and are thus more reliable and robust. Similarly, the playback devices for these memory cards need not contain movement mechanisms and are therefore also more reliable, robust, and, in general, less expensive than conventional players. The electronic memory devices and corresponding players are also generally much smaller than conventional discs or tapes and corresponding players, and generally consume less power, further increasing their suitability for use as portable playback systems.
One method for limiting the ability to copy the content material is a “check-out/check-in” system. In this, as in other protection schemes presented herein, it is assumed that the copying and playback devices are “conforming” devices, in that they conform to the standards used to protect copy-protected material. When a copy of the material is made from a providing device to a portable medium, the conforming providing device prevents additional copies from being made until the portable medium containing the copy is returned to the providing device. That is, the check-out/check-in system provides a “one-at-a-time”, or an “at-most-N-at-a-time”, copy scheme to limit the number of simultaneously available copies of protected content material.
A check-out/check-in system is susceptible to a variety of attacks intended to overcome the security provided by a check-out/check-in system. The most straightforward attack is one in which a non-conforming device is used to receive the material. After receiving the material, the non-conforming device provides unlimited copies. Another attack is one in which a non-conforming device “checks-in” material that another device received. A conforming device can receive/check-out the material, the non-conforming can “check-in” the material, and another conforming device can then receive the material, because the check-out/check-in system believes that the other copy has been returned. In this manner, an unlimited number of copies can be made to conforming devices, such as the aforementioned flash memory cards.